Non-Adhesional Mechanisms for Friction

There are mechanisms other than the adhesion of asperity contacts that can result in phenomenologically observable friction. The two most important, from an engineering viewpoint, are plowing and hysteresis loss. 

Only a brief presentation of the plowing mechanism is given here. The reader is referred to the description by Bowden and Tabor [22] for a fuller treatment. Let us consider a hard metal sphere of radius K pressed into a soft metal block by a load W (Fig. 8-19a). If A is the projected area of contact and p is the yield pressure of the softer metal, then 

This assumes that the surfaces are perfectly smooth so that the deformed area is identical with the contact area. Now let us cause the sphere to slide by applying the tangential force F. This force is comprised of two parts, one being the shear force 

If the plowing is accomplished by sliding a thin lamina (Fig. 8-19b), then the first term of Eqn 8-39 becomes negligible and the tangential force is 

The plowing force, therefore, is proportional to the third power of the track width. Experiments with a steel spade plowing through indium have confirmed this relation [22]. 

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